Polymeric organic materials that typically are used to make optical elements, transparent sheets and films, often have surfaces that are susceptible to abrasion and chemical attack. To prevent damage, such materials may be coated with a protective coating to improve their abrasion resistance.
Numerous protective coatings of various chemistries have been developed in the optical art. For example, coatings that incorporate epoxy-containing silane monomers, aluminum compounds and other silane monomers have been described in the literature. Coatings prepared from a colloidal dispersion of a water-insoluble dispersant such as aluminum oxide in a water-alcohol solution of selected organotrialkoxysilanes have also been developed. Hard coat compositions such as epoxy group-containing difunctional alkoxysilanes, tetrafunctional silanes, colloidal titania or alumina and curing catalysts are also among the conventional systems.
Incorporation of colorants, or tints, into certain abrasion resistant coatings has proven to be difficult. Often the tint application can be non-uniform, resulting in a “blotchy” appearance. Birefringence of coating layers has also been observed as an undesirable effect. It is particularly disadvantageous in fashion lenses, where aesthetics can be critical.
It would be desirable to provide optical articles having coatings that provide abrasion resistance while further allowing for homogeneous tintability, minimal birefringence, and compatibility with anti-reflective coatings.